Robustify error msg against more failure

When syncfolder() fails, we output an error message containing the
foldername per the localfolder variable. However, the localfolder
variable is assigned inside our try: block and when the error occurs
there, we will have no localfolder variable to use for output. This
caused the errormsg to cause an Exception itself which unhelpfully
distracts from the root cause of the error.

Reconstruct the folder name in a bit more complex way, but in a way so
it is guaranteed to work (by relying on parameters passed in to the
function).

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

offlineimap/accounts.py

@@ -420,8 +420,15 @@ def syncfolder(accountname, remoterepos, remotefolder, localrepos,
         if e.severity > OfflineImapError.ERROR.FOLDER:
             raise
         else:
-            ui.error(e, exc_info()[2], msg = "Aborting folder sync '%s' "
-                     "[acc: '%s']" % (localfolder, accountname))
+            #if the initial localfolder assignement bailed out, the localfolder var will not be available, so we need
+            ui.error(e, exc_info()[2], msg = "Aborting sync, folder '%s' "
+                     "[acc: '%s']" % (
+                    remotefolder.getvisiblename().\
+                        replace(remoterepos.getsep(), localrepos.getsep()),
+                    accountname))
+                    # we reconstruct foldername above rather than using
+                    # localfolder, as the localfolder var is not
+                    # available if assignment fails.
     except Exception, e:
         ui.error(e, msg = "ERROR in syncfolder for %s folder %s: %s" % \
                 (accountname,remotefolder.getvisiblename(),